1. Field of the Invention
Embodiments of the present invention relate to an EFEM (Equipment Front End Module) capable of circulating gas in a wafer transport chamber without exposing a wafer to the outside air during transportation.
2. Description of the Related Art
Conventionally, production of semiconductors has been carried out by various processing steps performed on a wafer as a substrate. In recent years, circuit miniaturization and high integration of elements have been increasingly promoted. It has been required to maintain a high level of cleanliness around a wafer to prevent adhesion of water and particles to a surface of a wafer. Further, to prevent changes in properties of a surface of a wafer, such as oxidization, it has been performed to make a periphery of a wafer vacuum or nitrogen atmosphere that is an inert gas.
In order to properly maintain such an atmosphere around a wafer, a wafer is managed by placing in a sealable storage pod called a Front-Opening Unified Pod (FOUP), and nitrogen is filled inside the pod. Further, to transfer a wafer between a FOUP and a processing apparatus for processing a wafer, an equipment front end module (EFEM) as disclosed in Japanese Unexamined Patent Application Publication No. 2012-49382 is provided. An EFEM constitutes a wafer transport chamber that is substantially closed inside a housing, comprises a load port that functions as an interface unit between the FOUP on one of opposite wall surfaces, and is connected to a load lock chamber that is a part of a processing apparatus on the other of the wall surfaces. In a wafer transport chamber, a wafer transport apparatus for transporting a wafer is provided. By using a wafer transport apparatus, a wafer is loaded and unloaded between a load lock chamber and a FOUP connected to a load port.
In other words, a wafer is taken out of the FOUP (a load port) that is one transfer position by using the wafer transport apparatus, and transported to the load lock chamber that is the other transfer position. The processing apparatus performs processing for a wafer transported through the load lock chamber within a processing apparatus called a process chamber. After the processing is completed, the wafer is taken out through the load lock chamber, and returned to the FOUP.
The interior of the processing apparatus is set to a special atmosphere, a vacuum or the like in accordance with the processing, to enable quickly the processing for a wafer. The interior of the wafer transport chamber in the EFEM is kept in a clean air atmosphere at a high level of cleanliness by introducing the air cleaned through a chemical filter or the like, to prevent contamination due to adhesion of particles or the like to the surface of a wafer during transport.
In recent years, as the cleanliness has been advanced more and more, although the cleanliness is relatively high in the wafer transport chamber of EFEM, the influence of the air atmosphere different from the interior of a FOUP or a processing apparatus has been concerned.
In other words, the air atmosphere is likely to permit adhesion of moisture and oxygen to the surface of a substrate, causing corrosion and oxidation. Further, when a corrosive gas or the like used in the processing apparatus remains on the surface of a wafer, it may cause corrosion of a wiring material on the wafer surface and deterioration of yield. Further, a corrosion element accelerates a corrosion reaction, and when both moisture and corrosive gas are present, corrosion may develop faster.
In addition, in a configuration that when transferring a wafer, a purge unit provided in a load port supplies a FOUP with nitrogen or the like as an inert gas to pressurize the interior of the FOUP, thereby preventing the air atmosphere in the wafer transport chamber from entering the FOUP, it is necessary to continue the supply of nitrogen to the FOUP until the wafer transfer is completed. Thus, the supplied nitrogen flows out to the wafer transport chamber, causing a problem of an increase in the use amount of nitrogen and an increase in the cost.
To avoid such a problem, the interior of the wafer transport chamber may be set to a nitrogen atmosphere as in the FOUP. However, by simply setting a nitrogen atmosphere upon start of the wafer transportation, the cleanliness in the wafer transport chamber decreases as time passes, there occurs a possibility of adhesion of particles to the wafer surface during transportation in the chamber, and the influence of corrosive gas or the like used in the processing apparatus increases. Further, when the nitrogen is always supplied to the wafer transport chamber, the use amount of nitrogen increases further, and the cost increase is not solved.
In addition, the above problem arises similarly during transportation of substrates other than a wafer, as long as the transportation is done in an atmosphere different from the processing and storage location.
Embodiments of the present invention have been made to solve efficiently the above problems. In particular, it is an object of the invention to provide an EFEM that is able to suppress adhesion of particles to a wafer, and properly control the properties of the wafer surface without exposing a wafer during transportation to a change in the surface properties or an atmosphere that causes adhesion of particles, while avoiding an increase in the cost.